Technical Abstract:
We have developed a pig caecal cannulation model which allows us to evaluate the effects in vivo of feed withdrawal on 1) the caecal environment, including pH and volatile fatty acid (VFA) concentration, and 2) the growth of foodborne pathogens in the caecum. In vitro studies evaluated growth of Yersinia enterocolitica and Salmonella typhimurium at 5 concentrations of VFA at 4 pH levels. Minimal growth occurred in VFA an pH levels which simulated the caecum of a well-fed pig. Maximal occurs in the absence of VFA (0 mM/ml) at pH 7.0. When cultures in the caecal contents of a fasted pig, Yersinia and Salmonella replicate and survive. In contrast, caecal contents of a well-fed pig inhibit their growth in vitro. When instilled directly in the pig caecum, Y. enterocolitica and S. typhimurium were detected in fecal and cecal samples for up to 1 month. Infected pigs were subjected to four cycles of interrupted feeding. No predictable change occurs in the number of Yersinia or Salmonella in the caecum or in feces of pigs subjected to interrupted feedings when compared with controls on a normal feeding regimen. In contrast, a fasting cycle predictably reduced volatile VFA and increased the pH of the caecum. Thus, the pig caecal cannulation model is a practical way of monitoring the long- term dynamics of growth and survival of foodborne pathogens in the live animal.